In the case of steaming yam, pieces of yam are easier to mature, which takes about 8 minutes. Thick yam can be steamed for a while, which takes about 15 minutes, while in the case of yam segments, it is best to steam for about 20 minutes. If you use a pressure cooker, it will be faster. Sheet 5 minutes, thick block 10 minutes, and cutting only takes about 15 minutes.
The reason why yam turns purple after steaming with skin.
Because of the browning of the enzyme. Because yam contains enzyme components, enzymatic browning will occur when it comes into contact with oxygen, and the color will turn black. When yam is cooked, there will be a lot of water vapor and air circulating, and after yam comes into contact with these air, enzyme browning will occur, which will lead to darker color.
Under normal circumstances, this is a normal phenomenon, but it should be noted that if the yam is cooked before or the yam heart turns purple and rotten, it should be carefully eaten.